Method and apparatus for improved plasma processing uniformity

ABSTRACT

A method and apparatus for generating and controlling a plasma ( 130 ) formed in a capacitively coupled plasma system ( 100 ) having a plasma electrode ( 140 ) and a bias electrode in the form of a workpiece support member ( 170 ), wherein the plasma electrode is unitary and has multiple regions (R i ) defined by a plurality of RF power feed lines ( 156 ) and the RF power delivered thereto. The electrode regions may also be defined as electrode segments ( 420 ) separated by insulators ( 426 ). A set of process parameters A={n, τ i , Φ i , P i , S; L i } is defined, herein n is the number of RF feed lines connected to the electrode upper surface at locations L i , τ i  is the on-time of the RF power for the i th  RF feed line, Φ i  is the phase of the i th  RF feed line relative to a select one of the other RF feed lines, P i  is the RF power delivered to the electrode through the i th  RF feed line at location L i , and S is the sequencing of RF power to the electrode through the RF feed lines. One or more of these parameters are adjusted so that operation of the plasma system results in a workpiece ( 176 ) being processed with a desired amount or degree of process uniformity.

[0001] This is a continuation of International Application No.PCT/US01/24491, filed on Aug. 6, 2001, and also claims benefit of U.S.application No. 60/223,834, filed Aug. 8, 2000, the contents of both ofwhich are incorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention pertains to plasma processing ofworkpieces, and in particular pertains to a method and apparatus forimproving the uniformity of plasma processing.

[0003] Ionized gas or “plasma” may be used during processing andfabrication of semiconductor devices, flat panel displays and otherproducts requiring etching or deposition of materials. Plasma may beused to etch or remove material from semiconductor integrated circuitwafers, or to sputter or deposit material onto a semiconducting,conducting or insulating surface. Creating a plasma for use inmanufacturing or fabrication processes typically is done by introducinga low-pressure process gas into a chamber surrounding a workpiece suchas an integrated circuit (IC) wafer. The atoms or molecules of thelow-pressure gas in the chamber are ionized to form plasma by a radiofrequency energy (power) source after the gas molecules enter thechamber. The plasma then flows over and interacts with the workpiece.The chamber is used to maintain the low pressures required for plasmaformation, to provide a clean environment for processing thesemiconductor devices and to serve as a structure for supporting one ormore radio frequency energy sources.

[0004] Plasma may be created from a low-pressure process gas by inducingan electron flow that ionizes individual gas atoms or molecules bytransfer of kinetic energy through individual electron-gas moleculecollisions. Typically, electrons are accelerated in an electric fieldsuch as one produced by radio frequency (RF) energy. This RF energy maybe low frequency (below 550 KHz), high frequency (e.g., 13.56 MHz), ormicrowave frequency (e.g., 2.45 GHz).

[0005] The two main types of etching in semiconductor processing areplasma etching and reactive ion etching (RIE). A plasma etching systemtypically includes a radio frequency energy source and a pair ofelectrodes. A plasma is generated between the electrodes, and theworkpiece (i.e., substrate or wafer) to be processed is arrangedparallel to one of the electrodes. The chemical species in the plasmaare determined by the source gas(es) used and the desired process to becarried out.

[0006] A problem that has plagued prior art plasma reactor systems isthe control of the plasma to obtain uniform etching and deposition. Inplasma reactors, the degree of etch or deposition uniformity isdetermined by the design of the overall system, and in particular by thedesign of the RF feed transmission and the associated control circuitry.

[0007] In a plasma reactor system, the electrode is connected to a RFpower supply. The technological trend in plasma reactor design is toincrease the fundamental RF driving frequency of the RF power supplyfrom the traditional value of 13.56 MHz to 60 MHz or higher. Doing soimproves process performance, but increases the complexity of reactordesign.

[0008] One approach to improving etch and deposition uniformity has beento use a multi-segment electrode. With reference to FIG. 1, plasmareactor system 8 comprises reactor chamber 10 having an interior 12,within which is arranged a segmented electrode 16 having separate thickconducting electrode segments 18 each with an upper surface 18U and alower surface 18L. A silicon slab or “facing” (not shown) may beattached to each of the lower surfaces 18L of the segmented electrode bysuitable attachment means to control contamination due to sputtering ofthe metal electrode. Electrode segments 18 are separated by an insulator20 and are powered by corresponding RF power supplies 26 via RF feedlines 30 connected to respective electrode segments. Power control toelectrode segments 18 is provided by a main control unit 36. Matchnetworks 40 arranged between RF power supplies 26 and electrode segments18 are tuned to provide the best match to the load associated with aplasma 50 formed in interior region 12, so as to optimize power transferto the plasma.

[0009] Reactor system 8 includes a workpiece support member 60 oppositesegmented electrode 16, upon which a workpiece 66, such as a wafer, issupported. The design of segmented electrode 16 is such that lowersurfaces 18L of electrode segments 18 interfaces with a vacuum region 70in interior region 12. This puts electrode segments 18 directly incontact with plasma 50 formed in vacuum region 70, although if siliconfacings as mentioned above (not shown) are used, the surfaces of thesilicon electrode facings will be directly in contact with plasma 50.Numerous seals (not shown) are required between insulators 20 and theelectrode segments, and between the chamber 10 and insulators 20, toisolate vacuum region 70.

[0010] Current plasma reactor systems can perform an etch process withapproximately 5% non-uniformity. This level of performance is sufficientto meet near-term needs for state-of-the-art process performance, butwill soon be inadequate as the demands on the manufacturing processincrease to require, on a routine basis, non-uniformity below 5%.

[0011] In light of the demands on improving process speed, onetechnological trend in plasma reactor design is to increase thefundamental RF frequency from the traditional value of 13.454 MHz to 60MHz or higher, as mentioned above. Doing so improves processperformance, but increases the complexity of reactor design. A secondtrend in reactor design is to have multiple electrodes, i.e., electrodesegments, such as those discussed above in connection with FIG. 1.However, multiple electrodes combined with increased operatingfrequencies mean that delivering the correct amount of RF power becomesmore complicated because of capacitive coupling between the electrodesegments and greater sensitivity to parasitic capacitive and inductiveelements. This effect is exacerbated by the shorter wavelengths ofhigher fundamental frequencies. The result is increased difficulty inreducing process non-uniformity.

[0012] In addition, current multi-segmented electrode plasma reactorsrequire a power supply for each electrode. Thus, if there are fiveelectrode segments, there must be five corresponding power supplies (orseparate amplifiers). This leads to high cost and increased maintenancerequirements and thus high wafer processing costs. This cost andincreased maintenance might be worthwhile if there were a way to improvethe performance of such a system to provide a higher degree of etch ordeposition uniformity beyond the present limits of existing plasmaprocessing systems.

BRIEF SUMMARY OF THE INVENTION

[0013] The present invention pertains to plasma processing ofworkpieces, and in particular pertains to a method and apparatus forimproving the uniformity of the plasma processing.

[0014] The present invention is a method of and apparatus for generatingand controlling a plasma formed in a capacitively coupled plasma systemhaving a plasma electrode and a bias electrode, wherein the plasmaelectrode has multiple regions defined by RF power feed lines, with thesize of each region being dependent on the amount of RF power deliveredthereto. The electrode regions can also be defined as electrode segmentsseparated by insulators. The RF power to each electrode region isindependently controlled. In particular, the amplitude, phase,frequency, and/or “on-time” during which the RF power is applied to eachRF feed line of the electrode can be varied, thereby affecting thespatial distribution of the plasma-exciting electric field and theplasma density (i.e., ion density) of the plasma.

[0015] Accordingly, a first aspect of the invention is an electrodeapparatus for use in plasma processing. The apparatus comprises aunitary electrode having an upper surface and a lower surface. A unitaryelectrode is an electrode, usually planar, for which the entireelectrode comprises either a single conductor or a plurality ofconductors that are interconnected by means of low resistance ohmiccontacts. A silicon facing; i.e., a so-called silicon electrode, can beattached by various attachment means to the lower surface of the unitaryelectrode in accordance with common practice. An RF multiplexer iselectrically connected to a plurality of locations on the electrodeupper surface via a corresponding plurality of RF feed lines. Theunitary electrode has a plurality of electrode regions corresponding tothe plurality of RF feed lines. These electrode regions are akin toelectrode segments of a segmented electrode, differing therefrom in thatthe electrode regions of a unitary electrode are not separated byinsulators. The apparatus can preferably include a plurality of matchnetworks arranged one in each RF feed line in said plurality of RF feedlines. The apparatus can also preferably include a control systemelectrically connected to the RF multiplexer, for controlling theoperation of said RF multiplexer when performing RF multiplexing.

[0016] A second aspect of the present invention is a plasma reactorsystem for processing a workpiece in a manner that achieves a highdegree of process uniformity. The system comprises a plasma chamberhaving sidewalls, an upper surface and a lower surface defining aninterior region capable of supporting plasma. A unitary electrode havingan upper surface is arranged within the interior region adjacent theupper wall. A RF multiplexer is electrically connected to a plurality oflocations on the upper surface of the unitary electrode via acorresponding plurality of RF feed lines. The electrode includes aplurality of electrode regions corresponding to the plurality of RF feedlines. Also included in the interior region adjacent the lower wall is aworkpiece support member for supporting the workpiece.

[0017] A third aspect of the present invention is a method ofdetermining a set of optimum plasma process parameters A*={n*, τ_(i)*,Φ^(i)*, P_(i)*, S*; L_(i)} for plasma processing a workpiece with a highdegree of uniformity. The method is carried out in a plasma reactorchamber having an electrode with an upper surface as part of a plasmareactor system. The parameters are defined as follows: n is the numberof RF feed lines connected to the electrode upper surface at locationsL_(i), τ_(i) is the on-time of the RF power for the i^(th) RF feed line,Φ^(i) is the phase of the i^(th) RF feed line relative to a selected oneof the other RF feed lines, P_(i) is the RF power delivered to theelectrode at location L_(i) through the i^(th) RF feed line, and S isthe sequencing of RF power to the electrode through the RF feed lines.The method comprises a first step of setting initial values for processparameters n, τ_(i), Φ_(i), P_(i), and S, and then a second step ofprocessing one or more workpieces while varying one or more of saidprocess parameters to determine the optimized set of process parametersA*={n*, τ^(i)*, Φ^(i)*, P_(i)*, S*} that achieve a processnon-uniformity less than the predetermined standard. The second stepincludes the steps of forming a first plasma within the reactor chamberhaving characteristics corresponding to the initial process parametersand processing a first workpiece for a predetermined process time,measuring the workpiece process uniformity, and comparing the workpieceprocess uniformity to a predetermined standard. If the workpiece processnon-uniformity is greater than the predetermined standard, then at leastone of the process parameters is changed and the above-steps repeated(using either the first workpiece or a different workpiece) until theworkpiece process non-uniformity is less than the predeterminedstandard.

[0018] A fourth aspect of the invention involves processing a workpieceusing the optimized process parameters deduced as described above inconnection with the third aspect of the invention.

[0019] A fifth aspect of the invention is the method of the first aspectof the invention, but carried out to achieve a desired degree of processuniformity. Such a method might be performed where there is a need topurposely provide a certain amount of process non-uniformity to counterother process effects.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0020]FIG. 1 is a schematic cross-sectional diagram of a prior artplasma reactor system having a segmented electrode comprising aplurality of electrode segments with corresponding RF power suppliesconnected thereto;

[0021]FIG. 2A is a schematic cross-sectional diagram of the plasmareactor system of the present invention having a unitary electrode withmultiple RF feed lines connected at one end to various locations on theunitary electrode upper surface, and connected at the opposite ends to aRF power multiplexer;

[0022]FIG. 2B is a block diagram of an embodiment of one component ofthe system of FIG. 2A;

[0023]FIG. 3 is a flow diagram of the method according to the presentinvention of optimizing the process parameters of the plasma reactorsystem of FIG. 2;

[0024]FIG. 4A is a schematic diagram of a first alternate embodiment forthe RF power sources and electrode of the present invention, whereinmultiple RF power supplies feed power through multiple match networks toelectrode segments of a multi-segment electrode;

[0025]FIG. 4B is a schematic diagram of a second alternate embodimentfor the RF power sources and electrode of the present invention, whereina single RF power supply feeds power through a match network and amultiplexer distributing power to electrode segments in a multi-segmentelectrode;

[0026]FIG. 4C is a schematic diagram of the first alternate embodimentfor the RF power sources and electrode of the present invention, whereinmultiple RF power supplies feed power through multiple match networks toa unitary electrode; and

[0027]FIG. 4D is a schematic diagram of the second alternate embodimentfor the RF power sources and electrode of the present invention, whereina single RF power supply feeds power through a match network and amultiplexer distributing power to electrode regions R_(i) of a unitaryelectrode.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention pertains to plasma processing ofworkpieces, and in particular pertains to a method and apparatus forimproving the uniformity of the plasma processing.

[0029] With reference to FIG. 2A, plasma reactor system 100 comprisesreactor chamber 102 with sidewalls 104, an upper wall 108 and a lowerwall 112 defining an interior region 120 capable of supporting plasma130. Arranged within interior region 120 near upper wall 108 is aunitary electrode 140 having an upper surface 140U and a lower surface140L and a periphery 144. Electrode 140 is referred to as the “plasmaelectrode”. Insulators 146 are arranged between electrode periphery 144and sidewalls 104 to electrically isolate electrode 140 from chamber102. System 100 further includes a RF power multiplexer 150. A RF powersupply 152 is included in RF multiplexer 150. Alternatively, an externalRF power supply (as illustrated by RF power supply 154) is provided.

[0030]FIG. 2B shows an exemplary layout of a multiplexer 150 acting todistribute RF power from a single RF generator 154 sequentially to aplurality of electrodes or electrode regions. Although only twoelectrodes are illustrated for the sake of simplicity, it will beunderstood that any number of electrodes can be supplied. In FIG. 2B acentral computer, or controller, 230 communicates with RF powergenerator 154, multiplexer 150 and one or more match networks 160.Multiplexer 150 is composed of an isolator and a coax switch. Theisolator can be a commercially available product of the type distributedby HD Communications Corporation (1 Comac Loop, Ronkonkoma, N.Y. 11779)who specializes in RF, microwave, fiber optic and wirelesscommunications products. In particular, that company distributes andcustom builds UHF, VHF, high power circulators and isolators. Forinstance, devices in the frequency ranges of (VHF) 66-88, 144-225 MHzand (FM) 88-108 MHz are currently available. The coax switch can be acommercially available product distributed by Texas Towers, inparticular the Ameritron RCS-8V. The specifications for the AmeritronRCS-8V are as follows: a frequency range of 0.5 to 450 MHz, powerhandling of 5000 W at 30 MHz, power handling of 1000 W at 150 MHz, <0.05dB insertion loss and 50 Ω impedance. Generator 154, match networks 160and the coax switch of multiplexer 150 are all connected to becontrolled by computer 230 to distribute power to the various electrodesin any desired pattern.

[0031] Reverting to FIG. 2A, system 100 further includes multiple (n) RFfeed lines 156 (e.g., 156 _(i), where i=1 to n) connected to multiplexer150 and that pass through tipper wall 108 and connect at their oppositeends to different locations L_(i) (e.g., L₁, L₂, . . . L_(n)) onelectrode upper surface 140U. RF power multiplexer 150 is a device thatdirects RF power to one or more of the RF feed lines 156 at a giventime. The locations L_(i) of RF feed lines 156 define correspondingelectrode regions R_(i) (e.g., R₁, R₂, . . . . R_(n)) to which RF poweris provided. The sizes of regions R_(i) depend on the amount of RF powerP_(i) provided, relative to the amount of power provided to adjacentregions but typically each of these regions extends over an area of theorder of the total electrode area divided by n. For a segmentedelectrode, when only a single electrode segment is powered, it is knownthat the highest process rate (etch or deposition rate) on a waferoccurs directly under that powered segment. Although a similar resultoccurs with a unitary electrode when a RF feed with its L_(i) axiallylocated is the only powered RF feed, when a RF feed with its L_(i)located off-axis is the only powered RF feed, the highest process rateon a wafer occurs at a location diametrically opposite to that L_(i).

[0032] System 100 also preferably includes match networks 160 arrangedin RF feed lines 156 between RF multiplexer 150 and electrode 140. Matchnetworks 160 are tuned to provide the best match to the load presentedby plasma 130 formed within interior region 120 so as to optimize powertransfer to the plasma.

[0033] Reactor system 100 further includes a workpiece support member170 arranged adjacent lower wall 112 opposite segmented electrode 140,capable of supporting a workpiece 176, such as a wafer, to be processed(e.g., etched or coated) by means of plasma 130.

[0034] System 100 also includes a workpiece handling system 180 inoperative communication with plasma chamber 102 (see dashed line 182),for placing workpieces 176 onto and removing workpieces 176 fromworkpiece support member 170. Also included is a gas supply system 190in pneumatic communication with chamber 102 via a gas supply line 194for supplying gas to chamber interior 120 to purge the chamber and tocreate plasma 130. The particular gases included in gas supply system190 depend on the application. However, for plasma etching applications,gas supply system 190 preferably includes such gases as chlorine,hydrogen-bromide, octafluorocyclobutane, and various other fluorocarboncompounds, etc. For chemical vapor deposition applications, gas supplysystem 190 preferably includes silane, ammonia, tungsten-tetrachloride,titanium-tetrachloride, and the like.

[0035] Further included in system 100 is a vacuum system 200 inpneumatic communication with chamber 102 via a vacuum line 204. Alsoincluded in system 100 is a workpiece support power supply 210electrically connected to workpiece support member 170, for electricallybiasing the workpiece support member. This electrical connection allowsworkpiece support member 170 to serve as a lower electrode, alsoreferred to as the “bias electrode”.

[0036] System 100 also includes a main control system 230, which is inelectronic communication with and controls and coordinates the operationof workpiece handling system 180, gas supply system 190, vacuum system200, workpiece support power supply 210, and RF power multiplexer 150through electrical signals. Main control system 230 thus controls theoperation of system 100 and the plasma processing of workpieces 176 inthe system, as described below.

[0037] In a preferred embodiment, main control system 230 is a computerwith a memory unit MU having both random-access memory (RAM) andread-only memory (ROM), a central processing unit CPU with amicroprocessor (e.g., a PENTIUM™ processor from Intel Corporation), anda hard disk HD, all electrically connected. Hard disk HD serves as asecondary computer-readable storage medium, and may be, for example, ahard disk drive for storing information corresponding to instructionsfor control system 230 to carry out the present invention, as describedbelow. Control system 230 also preferably includes a disk drive DD,electrically connected to hard disk HD, memory unit MU and centralprocessing unit CPU, wherein the disk drive is capable of accepting andreading (and even writing to) a computer-readable medium CRM, such as afloppy disk or compact disk (CD), on which is stored informationcorresponding to instructions for control system 230 to carry out thepresent invention. It is also preferable that control system 230 hasdata acquisition and control capability. A suitable control system 230is a computer, such as a DELL PRECISION WORKSTATION 610™, available fromDell Corporation, Dallas, Tex.

[0038] System 100 also includes a database 240 electrically connected to(or alternatively, integral to) control system 230 for storing datapertaining to the plasma processing of workpiece 176, and for alsoincluding predetermined sets of instructions (e.g., computer software)for operating system 100 via control system 230 to process theworkpieces.

[0039] Method of Operation

[0040] The operation of system 100 involves setting numerousprocess-related parameters that can be modified in optimizing RF powerdelivery to electrode 140 in a manner that allows the etch or depositionrate to be controlled to obtain a high degree of etch or depositionuniformity (i.e., non-uniformity less than 5%).

[0041] These process parameters are the number n of RF feed lines 156providing power to electrode 140, the power on-time τ_(i) for the i^(th)RF feed line (i=1 to n), the phasing Φ_(i) of the i^(th) RF feed line orcombinations of RF feed lines relative to a select one of the RF feedlines, the amount of power P_(i) delivered to the i^(th) RF feed line,and the sequence S of power P_(i) delivered to the electrode via each RFfeed line and hence to each electrode section R_(i). An additionalparameter, which is typically fixed but in certain cases can be varied,is the location L_(i) (L₁, L₂, . . . L_(n)) at which each of RF feedlines 156 is attached to upper surface 140U of electrode 140. Theseprocess parameters form a process parameter set A={n, τ_(i), Φ_(i),P_(i), S; L_(i)}. Any of the parameters in set A can be combined andvaried independently or in concert to achieve the desired workpieceuniformity requirements. These parameters can also be utilized toachieve differential workpiece processing when desired. In either case,the parameter set A that contains an optimized set of parameters isA*={n*, τ_(i)*, Φ_(i)*, P_(i) S*; L_(i)*}.

[0042] The optimum parameter set A* can be achieved empirically usingthe method comprising the following steps. With reference to the flowdiagram 300 of FIG. 3, once a workpiece is loaded onto workpiece supportmember 170, the first step 301 is setting the parameters n, τ_(i),Φ_(i), P_(i), S, and L_(i) to initial values. As mentioned above, L_(i)is typically fixed, but could be varied if the need arises, i.e., ifvarying the other process parameters does not result in an acceptableprocess uniformity. These initial values can be decided upon based ondata from previously run experiments stored in database 240 or throughthe assistance of computer modeling. The second step 302 is formingplasma 130 within interior region 120 based on the initial parametervalues set in step 301 and processing workpiece 176 with the plasma.Plasma 130 will have time-varying characteristics (e.g., plasma density,energy, etc.) corresponding to the initial values of the processparameters. The plasma characteristics (i.e. plasma density, energy,etc.) will vary in time in that, in particular, their spatialdistributions will vary in time throughout the process run due to the RFpower and/or other process parameter sequencing through the process run.For instance, a first electrode or electrode region is initially poweredfor a short time and corresponding to this condition there is aparticular spatial distribution of the plasma properties. This shortperiod of time is followed by a second short period of time during whicha second electrode or electrode region is powered with a differentcorresponding distribution of plasma properties. Each of these shortsteps adds to form the entire process run.

[0043] In second step 302, workpiece 176 is processed with plasma 130for a process time T_(P). During this time, RF multiplexer 150, underthe direction of controller 230, delivers an amount of RF power Pi toeach of the n RF feed lines 156 i for an “on-time”,τ_(i)<<τ_(P). Thisprocess is referred to herein as “RF power multiplexing.” Moreover, thesequencing S and phasing Φ_(i) of the n RF feed lines is also varied.The sequencing S can be such that only one location L_(i) at a time ispowered, or multiple locations L_(i) at one time are powered.

[0044] Thus, the etch or deposition distribution for the entire processtime τ_(P) can be considered as a linear superposition or a non-linearcombination of the etch distributions achieved by applying RF powerP_(i) to each RF feed line 156 based on the initial set of processparameters A. Here, the various parameters, such as the on-time τ_(i)can be different or the same for each RF feed line 156 _(i). Further,the amount of RF power P_(i) delivered can the same for all RF feedlines 156 _(i) as well.

[0045] With continuing reference to flow chart 300 of FIG. 3, the nextstep 303 is measuring the workpiece etch or deposition (i.e., process)uniformity. This is preferably accomplished using well-known opticalinterferometric techniques. The workpiece uniformity measurement isbased on the greatest etch depth/deposition thickness minus the smallestetch depth/deposition thickness divided by two times the mean etchdepth/deposition thickness of a large number of sites on the workpiecesurface. For a wafer with a diameter of about 20 centimeters, areasonable number of measurement sites is approximately 50 to 100. Thisresults in a quantitative workpiece uniformity value M_(U).

[0046] The next step 304 is assessing whether or not the workpieceuniformity measurement M_(U) is acceptable, i.e., less than a certainpredetermined standard (e.g., threshold) T_(U). It can be the case thata certain degree of non-uniformity is sought to counter other processingeffects, such as thin-film thickness variations across the surface ofthe workpiece. Such variations can be accounted for by measuring thespatial variation in uniformity as a function M_(U)(x,y) and comparingit to a predetermined standard represented by a spatially dependentfunction T(x,y) that corresponds to the non-uniformity profile sought.Here, it is assumed that the x-y plane lies in the plane of theworkpiece surface being processed.

[0047] If the result in step 304 is that the workpiece uniformity is notacceptable (i.e., the non-uniformity is greater than a predeterminedstandard), then in the next step 305, based on the results of step 304,at least one of the initial process parameters n, τ_(i), P_(i), S andL_(i) is changed in the effort to converge to the optimum set of processparameters, A*={n*, τ_(i)*, Φ_(i)*, P_(i)*, S*; L_(i)*}. Changing atleast one of the process parameters results in plasma 130 that hastime-varying characteristics different from the first-formed plasma 130.In this sense, plasma 130 represents first, second, third, etc. plasmassimilar to but different from one another that may need to be formed inthe process of deducing the optimum set of process parameters. Asmentioned above, one or more of the process parameters in set A can bechanged with the assistance of a computer program or algorithm thatmodels the plasma etch or deposition process.

[0048] One approach to finding the optimum set of parameters A* isthrough the use of a linear superposition or a non-linear combination ofetch or deposition rates based on each electrode region R_(i) For alinear superposition, this can be stated as:

PR(x,y)=(1/T _(P))Στ_(i)W_(i)[PR_(i)(x,y)],   Eq. 1

[0049] where PR(x,y) is the overall process rate, PR_(i)(x,y) is theprocess rate for each electrode region R_(i), T_(P) is the total processtime (i.e., the sum of the τ_(i)), and W_(i) is a weighting coefficient.The summation is performed by summing from 1 to n. The weightingcoefficient W_(i) is a function of at least one of the above-definedprocess parameters. For a linear optimization, W_(i) will typically bein the range of 0.9 to 1.1. Here, the weighting coefficients W_(i) maybe determined empirically based on the measurements made in step 303 byvarying one or more of the parameter values to arrive at the requiredweighting coefficients W_(i). Other more sophisticated computer modelsof the plasma etch process can also be used to assist in converging tothe optimum process parameter set A*. Also, it will be apparent to oneskilled in the art that non-linear equations can also be formed andsolved in the manner similar to Eq. 1 to find the set of optimumparameters A*.

[0050] It should be noted here that though there can be a total of n RFfeed lines 156 connected to upper surface 140U, fewer than all n RF feedlines may be activated. Here, it is assumed that n is the number of RFfeed lines 156 _(i) chosen to be activated. This number can be less thanthe total number of feed lines connected to upper surface 140U ofelectrode 140 because optimization of the process parameters can requirethat a certain group of the n RF feed lines not be activated.

[0051] Steps 302 to 305 are repeated until the measured workpieceuniformity M_(U) is acceptable, thereby defining the optimum processparameter set A*. Once the iteration of steps 301-305 is completed, thenin step 306 the optimum process parameter set A* is defined and recordedin database 240 and/or in control system 230 in memory unit MU. In thenext step 307, a workpiece 176, such as a semiconductor wafer, isprovided by placing the workpiece onto workpiece support member 170 viaworkpiece handling system 180. Then, in the next step 308, main controlsystem 230 controls the formation of an “optimized” version of plasma130 and controls the processing of workpiece 176 provided in step 307according to the optimum set of process parameters A* established instep 306 and recorded in database 240 and/or control system 230. Step308 is carried out for one or more workpieces 176. If workpiece 176needs to be processed with a new plasma process step requiring plasmadifferent from a particular form of plasma 130, then the steps of flowdiagram 300 are repeated for the new plasma process.

[0052] By way of example, n can be five, but might also range betweentwo and ten. A typical process time requires on the order of 60 seconds.If only one RF feed is excited at any given time, then if four sequencesS occur with five RF feeds, each sequence S will last for 15 sec. If allof the τ_(i) are equal, each τ_(i) will be three seconds. If the τ_(i)are too short, the demands on the RF matching network(s) can be toogreat; i.e., steady-state conditions may not be attained during the timeτ_(i).

[0053] With five RF feeds, one RF feed can be located on the axis ofsymmetry, with the other four located ninety degrees apart centered on acircle with a diameter approximately equal to ⅔ the wafer diameter. Theparameter Φ_(i) is meaningful only if two or more RF feeds are poweredsimultaneously. The value for P_(i) can be nearly equal, but need not beso. To provide high process throughput, it is preferable that the valuefor Pi should be about the same as the power that would be delivered viaa single feed to a conventional electrode.

[0054] Alternate Embodiments

[0055] The present invention, as described above, is a method andapparatus for delivering power at different locations to a unitaryelectrode. The process parameter optimization and operation methoddescribed above can also be applied to a number of alternate structuralembodiments as shown in FIGS. 4A-D, below, including a multi-segmentelectrode having a plurality of electrode segments.

[0056] With reference to FIG. 4A, multiple RF power supplies 400 feedpower through corresponding multiple RF feed lines 406 and multiplematch networks 410 to corresponding electrode segments 420 in amulti-segment electrode. Electrode segments 420 are separated byinsulators 426. In this first alternative embodiment, the number ofpower supplies, match networks, and electrode segments can be two orgreater. A control system 440 similar if not identical to control system230 is programmed to control the operation of RF power supplies 400 sothat they are multiplexed in a manner that replicates the RF powermultiplexing operation of RF multiplexer 150 of apparatus 100.

[0057] With reference now to FIG. 4B, a single RF power supply 400 feedspower through a single match network 410 and a multiplexer 450distributes power to electrode segments 420 of the multi-segmentelectrode via multiple RF feed lines 460. The number of electrodesegments 420 can be two or greater. As described above earlier inconnection with system 100, control system 440, similar if not identicalto control system 230, controls the operation of multiplexer 450 duringthe operation of system 100. In the system shown in FIG. 4B, matchnetwork 410 may need to be to programmed to adjust itself each timemultiplexer 450 switches.

[0058] With reference now to FIG. 4C, multiple RF power supplies 400feed power through multiple match networks 410 to a unitary electrode140, and control system 440, similar if not identical to control system230, is programmed to control the operation of RF power supplies 400 sothat they are multiplexed in a manner that replicates the RF powermultiplexing operation of RF multiplexer 150 of apparatus 100.

[0059] With reference now to FIG. 4D, there is shown a systemessentially the same as that described above in connection with system100, except that a single adjustable match network 410 is used insteadof a plurality of match networks. In the system of FIG. 4D, a single RFpower supply 400 feeds power through match network 410 and a multiplexer450 that distributes power to electrode regions R_(i) of a unitaryelectrode.

[0060] In alternate embodiments, the embodiments of FIGS. 4A and 4B areextended to the use coil antennas wherein an electrode 420 can be a RFantenna.

[0061] The many features and advantages of the present invention areapparent from the detailed specification and thus it is intended by theappended claims to cover all such features and advantages of thedescribed method that follow in the true spirit and scope of theinvention. Further, since numerous modifications and changes willreadily occur to those of ordinary skill in the art, it is not desiredto limit the invention to the exact construction and operationillustrated and described. Moreover, the methods and apparatus of thepresent invention, like related apparatus and methods used in thesemiconductor arts that are complex in nature, are often best practicedby empirically determining the appropriate values of the operatingprocess parameters, or by conducting computer simulations to arrive atthe optimum process parameters for a given application. Accordingly, allsuitable modifications and equivalents should be considered as fallingwithin the spirit and scope of the invention.

What is claimed is:
 1. An electrode apparatus for use in plasmaprocessing, comprising: a) a unitary electrode; b) a RF power supply;and c) a RF multiplexer electrically connected to said RF power supplyand to a plurality of locations on said unitary electrode via acorresponding plurality of RF feed lines thereby establishing aplurality of electrode regions corresponding to said plurality of RFfeed lines.
 2. An apparatus according to claim 1, further comprising aplurality of match networks arranged one in each of said plurality of RFfeed lines.
 3. An apparatus according to claim 2, further including acontrol system electrically connected for controlling the operation ofsaid RF power supply and said RF multiplexer.
 4. A plasma reactor systemfor processing a workpiece, comprising: a) a plasma chamber havingsidewalls, an upper wall and a lower wall defining an interior regioncapable of supporting a plasma; b) a unitary electrode having aplurality of electrode regions, arranged within said interior regionadjacent said upper wall; c) a RF multiplexer electrically connected tothe plurality of electrode regions of said unitary electrode via acorresponding plurality of RF feed lines; d) corresponding to saidplurality of RF feed lines; and e) a workpiece support member, arrangedin the interior region adjacent said lower wall, for supporting theworkpiece.
 5. A system according to claim 4, further comprising: f) acontrol system electrically connected to said RF multiplexer, forcontrolling the operation of said RF multiplexer when processing theworkpiece.
 6. A system according to claim 5, further comprising: g) aplurality of match networks each arranged one in a respective one ofsaid plurality of RF feed lines.
 7. A system according to claim 6,further comprising: h) a gas supply system in pneumatic communicationwith said chamber interior region, for supplying gas to said chamberinterior region.
 8. A system according to claim 7, further comprising:i) a workpiece support member RF power supply electrically connected tosaid workpiece support member, for electrically biasing said workpiecesupport member.
 9. A system according to claim 8, further comprising: j)a vacuum system pneumatically connected to said chamber interior region.10. A system according to claim 9, further comprising: k) a workpiecehandling system in operative communication with said workpiece supportmember, for providing the workpiece to the workpiece support member. 11.A system according to claim 5, further including a database electricallyconnected to said control system.
 12. A method of determining a set ofoptimum plasma process parameters A*={n*, τ_(i)*, Φ_(i)*, P_(i)*, S*;L_(i)*} for plasma processing, with a high degree of uniformity, aworkpiece in a plasma reactor chamber having an electrode with an uppersurface as part of a plasma reactor system, wherein n is the number ofRF feed lines connected to the electrode upper surface at locationsL_(i), t_(i) is the on-time of the RF power for the i^(th) RF feed line,Φ_(i) is the phase of the i^(th) RF feed line relative to a select oneof the other RF feed lines, Pi is the RF power delivered to theelectrode to location L_(i) through the i^(th) RF feed line, and S isthe sequencing of RF power to the electrode through the RF feed lines,the method comprising the steps of: a) setting initial values forprocess parameters n, τ_(i), Φ_(i), P_(i), and S; and b) processing oneor more workpieces while varying one or more of said process parametersto determine the optimized set of process parameters A*={n*, τ_(i)*,Φ_(i)*, P_(i)*, S*} that achieve a process non-uniformity less than apredetermined standard.
 13. A method according to claim 12, wherein saidstep b) includes the steps of: i) forming a first plasma within thereactor chamber having characteristics corresponding to said processparameters and processing a first workpiece for a predetermined processtime; ii) measuring the workpiece process uniformity; and iii) comparingthe workpiece process uniformity to a predetermined standard.
 14. Amethod according to claim 13, wherein said step b) further includes thestep of: iv) reducing the workpiece process non-uniformity by changingat least one of said process parameters and repeating said steps i)through iii) using one of said first workpiece and a workpiece otherthan said first workpiece, until the workpiece process non-uniformity isless than said predetermined standard.
 15. A method according to claim12, wherein in said steps a) and b), the locations L_(i) of the RF feedlines are parameters in the set A of process parameters that can bevaried.
 16. A method according to claim 12, wherein the initial processparameter values are determined with the assistance of computermodeling.
 17. A method according to claim 12, wherein said step b)includes use of a linear processing model as a basis for varying atleast one of the process parameters.
 18. A method according to claim 12,wherein said step b) includes use of a nonlinear processing model as abasis for varying at least one of the process parameters.
 19. A methodaccording to claim 12, wherein said step b) includes providing RF powerP_(i) to a plurality of electrode segments in a multi-segment electrodeby multiplexing RF power via RF power multiplexing.
 20. A methodaccording to claim 19, wherein said RF power multiplexing isaccomplished by programming a control system electrically connected to aplurality of RF power supplies and electronically controlling theactivation of the RF power supplies.
 21. A method according to claim 12,wherein said step b) involves providing RF power P_(i) to a unitaryelectrode via RF power multiplexing.
 22. A method of processing aworkpiece to be processed according to claim 12, further including thesteps, after said step b), of: c) providing the workpiece to beprocessed in the reactor chamber; d) forming an optimized plasma withthe process chamber using the set of optimized process parametersdetermined in said step b); and e) processing the workpiece to beprocessed with the optimized plasma.
 23. A method of determining a setof optimum plasma process parameters A*={n*, τ_(i)*, Φ_(i)*, P_(i)*, S*;L_(i)*} for plasma processing, with a desired degree of uniformity, aworkpiece in a plasma reactor chamber having an electrode with an uppersurface as part of a plasma reactor system, wherein n is the number ofRF feed lines connected to the electrode upper surface at locationsL_(i), τ_(i) is the on-time of the RF power for the i^(th) RF feed line,τ_(i) is the phase of the i^(th) RF feed line relative to a select oneof the other RF feed lines, P_(i) is the RF power delivered to theelectrode to location L_(i) through the i_(th) RF feed line, and S isthe sequencing of RF power to the electrode through the RF feed lines,the method comprising the steps of: a) setting initial values forprocess parameters n, τ_(i), Φ_(i), P_(i), and S; and b) processing oneor more workpieces while varying one or more of said process parametersto determine the optimized set of process parameters A*={n*, τ_(i)*,Φ_(i)*, P_(i), S} that achieve a desired process uniformity.
 24. Amethod according to claim 23, wherein said step b) includes the stepsof: i) forming a first plasma within the reactor chamber havingcharacteristics corresponding to said process parameters and processinga first workpiece for a predetermined process time; ii) measuring theworkpiece process uniformity; and iii) comparing the workpiece processuniformity to a predetermined standard.
 25. A method according to claim23, wherein said step b) further includes the step of: iv) reducing theworkpiece process non-uniformity by changing at least one of saidprocess parameters and repeating said steps i) through iii) using one ofsaid first workpiece and a workpiece other than said first workpiece,until the workpiece process non-uniformity is less than saidpredetermined standard.
 26. A method of processing a workpiece to beprocessed according to claim 23, further including the steps, after saidstep b), of: c) providing the workpiece to be processed in the reactorchamber; d) forming an optimized plasma with the process chamber usingthe set of optimized process parameters determined in said step b); ande) processing the workpiece to be processed with the optimized plasma.